Mass flow meters for flowing media that work on the Coriolis Principle are known in various embodiments (see, for example, German Disclosure Documents 26 29 833, 28 22 087, 28 33 037, 29 38 498, 30 07 361, 33 29 544, 34 43 234, 35 03 841, 35 05 166, 35 26 297, 37 07 777, 39 16 285 and 40 16 907, European Disclosure Documents 0 083 144, 0 109 218, 0 119 638, 0 196 150, 0 210 308, 0 212 782, 0 235 274, 0 239 679, 0 243 468, 0 244 692, 0 271 605, 0 275 367 and 0 282 522, as well as U.S. Pat. Nos. 4,491,009, 4,628,744 and 4,666,421), and are increasingly being used in practice.
In mass flow meters for flowing media that work on the Coriolis Principle, there is a basic difference between those instruments whose Coriolis line is designed as a straight pipe and others whose Coriolis line is designed as a--single or multiple--curved pipe and as a pipe loop. For the mass flow meters in question, there is also a difference between those that have only one Coriolis line and those that have two Coriolis lines; in designs with two Coriolis lines, they may be connected in series or in parallel to one another, according to the flow technology. All these different flow meter embodiments have advantages and disadvantages.
The embodiments of mass flow meters in which the Coriolis line is designed as a straight pipe and in which Coriolis lines are designed as straight pipes are simple to produce as far as their mechanical constructions are concerned and consequently cost relatively little. For example, the inner surfaces of each pipe can be processed easily, e.g., polished. Also, their pressure loss is low. They are disadvantaged in that at a certain structural length, their natural frequency is relatively high. Embodiments of the mass flow meters in which the Coriolis line(s) is/are designed as a curved pipe(s) have disadvantages where the embodiments with straight pipe(s) have advantages; but their advantage is that at a certain structural length, their natural frequency is relatively low.
Mass flow meters that work on the Coriolis Principle have an oscillating system or one capable of oscillating. The Coriolis line has a natural line frequency and an oscillator oscillates the line at a selected driving frequency. Usually, the oscillator oscillates at the natural line frequency, i.e., the Coriolis line is excited by the oscillator at an oscillation frequency that corresponds to the natural frequency for the Coriolis line. The Coriolis natural frequency should be the oscillation frequency preferably excited by the Coriolis force. The fact that mass flow meters that work on the Coriolis Principle represent an oscillating system or one capable of oscillating leads to the fact that, on one hand, the oscillations are transferred to the line into which the mass flow meter is inserted, and that, on the other hand, oscillations in the line in which the mass flow meter is inserted are transferred to the mass flow meter and distort the measurement results; naturally neither one of these effects is desired.